Melt-spun polysulfone semipermeable membranes and methods for making the same

ABSTRACT

The present invention discloses, inter alia, a composition useful for producing a hemogeneous, semipermeable membrane, the composition comprising (1) a polysulfone compounds, (2) a solvent, such as sulfolane, antypyrine, δvalerolactam, diethyl phthalate, and mixtures thereof, and (3) a non-solvent, such as poly(ethylene glycol), di(ethylene glycol), tri(ethylene glycol), glycerol, and mixtures thereof. Another aspect of this invention discloses methods for fabricating semipermeable membranes by homogeneously mixing the composition of the polysulfone compound, solvent, and non-solvent, melting the composition, and melt-spinning the molten composition. Another aspect of the present invention includes homogeneous, melt-spun, semipermeable membranes useful for liquid separation processes, such as, but not limited to, microfiltration, ultrafiltration, dialysis, and reverse osmosis.

This application is a Continuation of prior application Ser. No.:09/317,657 filed May 24, 1999 now U.S. Pat. No. 6,218,441, which is a:Divisional of prior application Ser. No.: 08/932,680 filed Sep. 18, 1997now abandoned.

FIELD OF THE INVENTION

The present invention concerns polysulfone semipermeable membranes andmethods for making the same. More particularly, the invention pertainsto melt-spun polysulfone semipermeable membranes.

BACKGROUND OF THE INVENTION

Contemporary semipermeable membranes are available in a variety of formssuch as sheets, tubes, and hollow fibers. A “hollow fiber” is generallya hollow cylindrical structure in which the wall functions as apermeable, non-permeable, or semipermeable (i.e., selectively permeable)membrane depending upon the application. Generally, hollow fibers areused as cylindrical membranes that permit selective exchange ofmaterials across the walls.

Liquid-separation processes utilizing membranes having selectivepermeabilities, such processes including ultrafiltration,microfiltration, dialysis, reverse osmosis, or the like, require avariety of materials adapted for diversified applications. For example,semipermeable membranes are currently favored for use in extracorporealblood treatments including hemodialysis, hemofiltration, andhemodiafiltration. In such cases, the membranes typically comprisehollow fibers bundled together and assembled in a casing in a mannerallowing blood to flow simultaneously in a parallel manner through thelumina of the fibers while a blood-cleansing liquid is simultaneouslypassed through the casing so as to bathe the exterior surfaces of thehollow fibers with the liquid.

Compounds utilized for selectively permeable membranes have includedpolymers, such as cellulose, cellulose acetate, polyamide,polyacrylonitrile, polyvinylalcohol, polymethyl methacrylate,polysulfone, polyolefin, or the like, depending upon the use of themembranes. Polysulfone compounds are of particular interest as theyhave, inter alia, excellent physical and chemical properties, such asresistance to heat, resistance to acids, resistance to alkali, andresistance to oxidation. Polysulfone compounds have been found to bebiocompatible, capable of forming excellent pores and interstitia, andchemically inert to such compounds as bleach, disinfectants, and saltsolutions. Polysulfone compounds can be sterilized by a number ofmethods, such as ethylene oxide (EtO), gamma irradiation, steamautoclave, and heated citric acid. Additionally, polysulfone compoundspossess sufficient strength and resistance to wear to withstand repeateduse and sterilization cycles.

Conventionally, polysulfone hollow fibers have been formed bysolution-spinning techniques. Producing polysulfone hollow fibers bysolution-spinning techniques typically involves dissolving a polysulfonecompound in a relatively large amount of an aprotic solvent and anon-solvent, then extruding the solution through a spinneret. Forsolution spinning, a “solvent” is a compound in which the polysulfonecompound substantially dissolves at the membrane-fabrication temperature(i.e., ambient temperature). For solution spinning, a “non-solvent” is acompound in which the polysulfone compound is substantially insoluble atthe membrane-fabrication temperature. For solution-spinning techniques,the solvents must be sufficient to substantially dissolve thepolysulfone compound and produce a homogeneous liquid at ambienttemperature (membrane fabrication temperature).

The solvents and non-solvents utilized for solution-spinning techniquesrequire that the membranes be extensively leached and rinsed afterfabrication, as even residual amounts left in the membranes can causeunacceptable contamination of fluids treated using the membranes.Avoiding such contamination is particularly important in membranes usedfor the treatment of blood by dialysis or the desalination of water byreverse osmosis. When fabricating hollow-fiber membranes utilizingsolution spinning techniques, removal of the core liquid used to formthe fiber lumen is especially difficult. Following removal of thesolvents, non-solvents, and core liquid, a non-volatile, water-solublecompound must then be added to preserve the membrane pore structureprior to drying the membrane. The non-volatile material also serves as asurfactant for later rewetting of the membranes. Such a process is knownas “replasticization.”

Solution-spinning techniques require the inclusion of large amounts ofsolvents and non-solvents many of which are generally toxic and can bedifficult to extract from the resulting polysulfone fiber. Moreover, thesignificant amount and high level of toxicity of certain solvents andnon-solvents removed from the fibers may create a hazardouswaste-disposal problem.

Moreover, conventional solution-spinning techniques produce asymmetricpolysulfone membranes (i.e., non-homogeneous membrane porosityprogressing through the thickness dimension of the membrane). That is, anon-homogeneous membrane has a dense skin or micro-porous barrier layeron one (or both) of the major surfaces of the membrane. The dense skinor micro-porous barrier layer comprises a relatively small portion ofthe membrane but contributes a disproportionally large amount of controlon the permeability characteristics of the membrane.

Accordingly, there is a need for a polysulfone composition and simplemethod for the production of polysulfone semipermeable membranes whichcomposition and method minimizes toxic waste by-products. Additionally,there is a need for a method for the production of polysulfonesemipermeable membranes wherein the solvents, non-solvents, andprocessing aids used in the manufacture of the membranes are easilyremoved from the membranes after fabrication and/or are of relativelylow toxicity. There is also a need for polysulfone semipermeablemembranes having a more uniform structure throughout the thicknessdimension (i.e., a homogeneous polysulfone membrane) so that the entirethickness dimension controls the permeability of the membrane.

SUMMARY OF THE INVENTION

In general, the present invention provides, inter alia, a novel methodand polysulfone composition for preparing a homogeneous, semipermeablepolysulfone membrane by melt-spinning. The polysulfone compositioncomprises a liquid mixture of a polysulfone compound, a solvent and,optionally, a non-solvent that are relatively non-toxic and thatpreferably do not deleteriously affect the environment.

The solvent may be selected from the group consisting of tetramethylenesulfone (“sulfolane”); 3-methyl sulfolane; benzophenone;n,n-dimethylacetamide; 2-pyrrolidone; 3-methylsulfolene; pyridine;thiophene; o-dichlorobenzene; 1-chloronaphthalene; methyl salicylate;anisole; o-nitroanisole; diphenyl ether; diphenoxy methane;acetophenone; p-methoxyphenyl-2-ethanol; 2-piperidine; antipyrine;diethyl phthalate; diphenyl sulfone; diphenyl sulfoxide; phthalic acid,dioctyl ester; phthalic acid, dimethyl ester; phthalic acid, diethylester; phthalic acid, dibutyl ester; phthalic acid, bis(2-ethylhexyl)ester; phthalic acid, benzyl butyl ester; and phenyl sulfide.

Especially good results have been achieved when the solvent comprisessulfolane, 2,3-dimethyl-1-phenyl-3-pyrazolin-5-one (antipyrine),2-piperidine (6-valerolactam, diethyl phthalate, or a mixture thereof.

The non-solvent may be selected from the group consisting ofpoly(ethylene glycol), di(ethylene glycol), tri(ethylene glycol),glycerol, 1,1-diethylurea; 1,3-diethylurea; dinitrotoluene; 1,2-ethanediamine; diphenylamine; toluenediamine; o-toluic acid; m-toluic acid;toluene-3,4-diamine; dibutyl phthalate; piperidine; decalin;cyclohexane; cyclohexene; chlorocyclohexane; “cellosolve” solvent;n,n-dimethylbenzylamine; paraffin; mineral oil; mineral wax; tallowamine; triethanol amine; lauryl methacrylate; stearic acid; ethyleneglycol; tetra(ethylene glycol); diethyl adipate; d-sorbitol;chlorotriphenyl stannane; resorcinol; 2-methyl-8-quinolinol; quinaldine;4-phenylpyridine; phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl)ester; N,N-dimethyl-p-phenylene diamine; 2,6-dimethoxyphenol;4-allyl-2-methoxyphenol; phenanthridine; 2-naphthylamine;1-naphthylamine; 1-naphthol; 2-naphthalenethiol; 1-bromonaphthalene;levulinic acid; phenyl pyrrol-2-yl ketone; phenyl 4-pyridyl ketone;isothiocyanic acid, m-nitrophenyl ester; 2-methyl-1H-indole; 4-methylimidazole; imidazole; 1,7-heptanediol; 9H-fluoren-9-one; ferrocene;2,2′,2″-nitrilotriethanol; 2,2′-iminodiethanol; dibenzofuran;cyclohexaneacetic acid; cyanamide; courmarin; 2,2′-bipyridine; benzoicacid; benzenepropionic acid; o-dinitrobenzene;9-methyl-9-azabicyclo(3.3.1)nonan-3-one; chlorodiphenylarsine; antimonybromide; p-anisidine; o-anisaldehyde; adiponitrile; p-aminoacetophenone; monoacetin; diacetin; triacetin; pentoxane;4-benzoylbiphenyl; methyl oleate; triethylphosphate; butyrolactone;terphenyl; tetradecanol; polychlorinated biphenyl (“Aroclor 1242”);myristic acid; methacrylic acid, dodecyl ester; isocyanic acid,methylenedi-p-phenylene ester; 2-((2-hexyloxy)ethoxy) ethanol; 4-nitrobiphenyl; benzyl ether; benzenesulfonyl chloride;2,4-diisocyanato-1-1-methyl benzene; adipic acid, diethyl ester;2′-nitro-acetophenone; 1′-acetonaphthone; tetradecanone;(dichlorophenyl)trichlorosilane; dichlorodiphenyl silane;phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester; phosphoricacid, tri-o-tolyl ester; phosphoric acid, triphenyl ester; phosphoricacid, tributyl ester; phenyl phosphorous dichloride; p-nitrophenol;isocyanic acid, methyl-m-phenylene ester; 2,2′-iminodiethanol;N-(2-aminoethyl)-N′-(2-((2-aminoethyl)amino)ethyl) 1,2-ethanediamine;2,6-di-tert-butyl p-cresol; chloro biphenyl; 4-biphenylamine; benzylether; benzenesulfonyl chloride; 1,2-(methylenedioxy)-4-propenylbenzene; 2,4-diisocyanato-l-methyl benzene; chlorodinitro benzene (mixedisomers); hexahydro 2H-azepin-2-one; 4,4′-methylenedianiline;1′-acetonaphthone; mercapto acetic acid; and acetanilide. Especiallygood results have been achieved when the non-solvent comprisespoly(ethylene glycol), di(ethylene glycol), tri(ethylene glycol),glycerol, or a mixture thereof.

The solvent and non-solvent are present in a ratio useful to form asemipermeable, polysulfone membrane useful for performingliquid-separation processes.

According to another aspect of the invention, a “melt-spinning” or“melt-extrusion” method is provided for producing semipermeable,polysulfone membranes. The melt-spinning method includes the steps of:(1) forming a composition comprising a polysulfone compound, a solventselected from the foregoing group of candidate solvents and preferablyselected from the group consisting of tetramethylene sulfone,antypyrine, δ-valerolactam, diethyl phthalate, and mixtures thereof,and, optionally, a non-solvent selected from the foregoing group ofcandidate non-solvents and preferably selected from the group consistingof poly(ethylene glycol), di(ethylene glycol), tri(ethylene glycol),glycerol, and mixtures thereof; (2) heating the composition to atemperature at which the composition becomes a homogeneous liquid (i.e.,a temperature greater than ambient); (3) extruding the compositionthrough an extrusion die (such as a single or multi-holed hollow-fiberdie (termed a “spinneret”); and (4) passing the extrudate through aquench zone in which the extrudate gels and solidifies, thereby formingthe membrane.

According to another aspect of the present invention, melt-spun,semipermeable, polysulfone membranes are provided having a uniformstructure throughout the thickness dimension of the membrane (i.e., a“homogeneous” membrane structure) useful for liquid separations, suchas, but not limited to, microfiltration, ultrafiltration, reverseosmosis, and dialysis.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a preferred embodiment of the process for fabricatinghomogeneous polysulfone hollow fibers (as a representative membraneconfiguration) according to the present invention.

FIG. 2 illustrates an alternative process for fabricating homogeneouspolysulfone hollow fibers according to the present invention

FIG. 3 is a three-component diagram showing the proportions ofpolysulfone compound, solvent, and non-solvent which are combined inrepresentative melt-spin compositions according to the invention.

FIG. 4 is a scanning electron microscope photograph of a representativehomogeneous, polysulfone hollow fiber according to the presentinvention.

FIG. 5 is a schematic diagram of a hemodialyzer including homogeneouspolysulfone hollow-fiber membranes of the present invention.

DETAILED DESCRIPTION

This invention encompasses, inter alia, compositions useful for forming,by melt-spinning, polysulfone semipermeable membranes. The compositionscomprise a polysulfone compound, a solvent and, optionally, anon-solvent. In the composition, the solvent and optional non-solventare present in a ratio useful to form a semipermeable membrane usefulfor performing liquid separation processes. Membranes that are melt-spunusing such compositions are homogeneous. That is, the melt-spunmembranes are symmetric such that the membranes have a substantiallyuniform structure throughout the thickness dimension of the membranes,as illustrated in the scanning electron microscope photograph in FIG. 4of a hollow fiber made using such a composition. As defined herein, a“homogeneous” polysulfone membrane is a membrane in which each portionor section of the membrane contributes its substantially proportionalshare to the permeability characteristics of the membrane.

Polysulfone compounds and their synthesis are well-known in the art.Preferred polysulfone compounds useful in this invention satisfy theformula:R₁—SO₂—R₂wherein R₁ and R₂ (which can be the same or different) are groups suchas alkanes, alkenes, alkynes, aryls, alkyls, alkoxys, aldehydes,anhydrides, esters, ethers, and mixtures thereof, each such group havingfifty or fewer carbon atoms and including both straight-chained andbranched-chained structures. Preferred polysulfone compounds useful inthis invention have a melt flow index (MFI) in a range of from about 1.7dg/min to about 9.0 dg/min as measured according to the AmericanStandard Test Method (ASTM) for Flow Rates of Thermoplastics byExtrusion Plastometer, ASTM D 1238-94a. Good results have been achievedwhen the polysulfone compounds have a MFI of from about 2.0 dg/min toabout 5.0 dg/min. Preferred polysulfone compounds useful in thisinvention include, but are not limited to polyarylsulfones, for example,bisphenol A polysulfone, polyether sulfone, polyphenyl sulfone, andmixtures thereof. Especially good results have been achieved utilizingbisphenol A polysulfone.

A “solvent for the polysulfone compound” is defined herein as a compoundhaving the following characteristics: a boiling point of at least about150° C., a solvating power to dissolve from about 8 weight percent toabout 80 weight percent of the polysulfone compound at a temperature ina range from about 50° C. to about 300° C. The solvent preferably candissolve from about 8 weight percent to about 80 weight percent of apolyarylsulfone.

Candidate solvents useful in this invention include, but are not limitedto, tetramethylene sulfone; 3-methyl sulfolane; benzophenone;n,n-dimethylacetamide; 2-pyrrolidone; 3-methylsulfolene; pyridine;thiophene; o-dichlorobenzene; 1-chloronaphthalene; methyl salicylate;anisole; o-nitroanisole; diphenyl ether; diphenoxy methane;acetophenone; p-methoxyphenyl-2-ethanol; 2-piperidine; antipyrine;diethyl phthalate; diphenyl sulfone; diphenyl sulfoxide; phthalic acid,dioctyl ester; phthalic acid, dimethyl ester; phthalic acid, diethylester; phthalic acid, dibutyl ester; phthalic acid, bis(2-ethylhexyl)ester; phthalic acid, benzyl butyl ester; phenyl sulfide. Especiallypreferred solvents useful in this invention include, but are not limitedto, tetramethylene sulfone (“sulfolane”), antipyrine, δ-valerolactam,diethyl phthalate, and mixtures thereof. Especially good results havebeen achieved utilizing tetramethylene sulfone as the solvent.

A “non-solvent for the polysulfone compound” is defined herein as acompound having the following characteristics: a boiling point of atleast about 150° C., a solvating power sufficiently low to dissolve lessthan about 5 weight percent of the polysulfone compound at a temperaturein a range from about 50° C. to about 300° C.

Candidate non-solvents useful in this invention are 1,1-diethylurea;1,3-diethylurea; dinitrotoluene; 1,2-ethane diamine; diphenylamine;toluenediamine; o-toluic acid; m-toluic acid; toluene-3,4-diamine;dibutyl phthalate; piperidine; decalin; cyclohexane; cyclohexene;chlorocyclohexane; “cellosolve” solvent; n,n-dimethylbenzylamine;paraffin; mineral oil; mineral wax; tallow amine; triethanol amine;lauryl methacrylate; stearic acid; di(ethylene glycol); tri(ethyleneglycol); ethylene glycol; poly(ethylene glycol); tetra(ethylene glycol);glycerin; diethyl adipate; d-sorbitol; chlorotriphenyl stannane;resorcinol; 2-methyl-8-quinolinol; quinaldine; 4-phenylpyridine;phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester;N,N-dimethyl-p-phenylene diamine; 2,6-dimethoxyphenol;4-allyl-2-methoxyphenol; phenanthridine; 2-naphthylamine;1-naphthylamine; 1-naphthol; 2-naphthalenethiol; 1-bromonaphthalene;levulinic acid; phenyl pyrrol-2-yl ketone; phenyl 4-pyridyl ketone;isothiocyanic acid, m-nitrophenyl ester; 2-methyl-1H-indole; 4-methylimidazole; imidazole; 1,7-heptanediol; 9H-fluoren-9-one; ferrocene;2,2′,2″-nitrilotriethanol; 2,2′-iminodiethanol; dibenzofuran;cyclohexaneacetic acid; cyanamide; courmarin; 2,2′-bipyridine; benzoicacid; benzenepropionic acid; o-dinitrobenzene;9-methyl-9-azabicyclo(3.3.1)nonan-3-one; chlorodiphenylarsine; antimonybromide; p-anisidine; o-anisaldehyde; adiponitrile; p-aminoacetophenone; monoacetin; diacetin; triacetin; pentoxane;4-benzoylbiphenyl; methyl oleate; triethylphosphate; butyrolactone;terphenyl; tetradecanol; polychlorinated biphenyl (“Aroclor 1242”);myristic acid; methacrylic acid, dodecyl ester; isocyanic acid,methylenedi-p-phenylene ester; 2-((2-hexyloxy)ethoxy) ethanol; 4-nitrobiphenyl; benzyl ether; benzenesulfonyl chloride;2,4-diisocyanato-1-1-methyl benzene; adipic acid, diethyl ester;2′-nitro-acetophenone; 1′-acetonaphthone; tetradecanone;(dichlorophenyl)trichlorosilane; dichlorodiphenyl silane;phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester; phosphoricacid, tri-o-tolyl ester; phosphoric acid, triphenyl ester; phosphoricacid, tributyl ester; phenyl phosphorous dichloride; p-nitrophenol;isocyanic acid, methyl-m-phenylene ester; 2,2′-iminodiethanol;N-(2-aminoethyl)-N′-(2-((2-aminoethyl)amino)ethyl) 1,2-ethanediamine;2,6-di-tert-butyl p-cresol; chloro biphenyl; 4-biphenylamine; benzylether; benzenesulfonyl chloride; 1,2-(methylenedioxy)-4-propenylbenzene; 2,4-diisocyanato-1-methyl benzene; chlorodinitro benzene (mixedisomers); hexahydro 2H-azepin-2-one; 4,4′-methylenedianiline;1′-acetonaphthone; mercapto acetic acid; and acetanilide. Especiallypreferred non-solvents useful in this invention include, but are notlimited to, poly(ethylene glycol), di(ethylene glycol), tri(ethyleneglycol), glycerol, and mixtures thereof.

The concentrations of the components in the composition may vary and aredependent upon variables many of which can be readily worked out withsimple bench experiments. For example, miscibility of the composition atthe melt-extrusion temperature is one factor to be considered indetermining a suitable component concentration. Miscibility ofpolysulfone compound solutions can be readily determined empirically bymethods known in the art. (Whether or not the components of acomposition are miscible is readily apparent.) The end use of themembrane is another factor in determining the appropriate blendcomposition because the preferred pore size of the membrane andtransport rate of liquids and solutes through the membrane varydepending upon the intended fiber end use.

In the case of membranes useful for microfiltration of liquids, theconcentration of the polysulfone compound is preferably at least about 8weight percent, more preferably at least about 12 weight percent. Theconcentration of the solvent is preferably at least about 40 weightpercent, more preferably at least about 60 weight percent. Theconcentration of the non-solvent, if present, is preferably at leastabout 1 weight percent, and more preferably at least about 5 weightpercent.

In the case of membranes useful for ultrafiltration or dialysis, theconcentration of the polysulfone compound is preferably at least about18 weight percent, more preferably at least about 25 weight percent. Theconcentration of the solvent is preferably at least about 40 weightpercent, more preferably at least about 45 weight percent. Concentrationof the non-solvent, if present, is preferably at least about 1 weightpercent, more preferably at least about 5 weight percent.

If the non-solvent is present, solvent to non-solvent ratios (i.e., asolvent to non-solvent ratio “sufficient to form a semipermeablemembrane useful for liquid separation processes”) are preferably about0.95:1 to about 80:1, and more preferably about 2:1 to about 10:1. Forexample, as shown in FIG. 3, for a three-component composition (formelt-spinning polysulfone hollow fibers) comprising bisphenol Apolysulfone, sulfolane (the solvent), and poly(ethylene glycol) (thenon-solvent), acceptable amounts of the polysulfone compound, solvent,and non-solvent lie within the area bounded by the extremes of eachcomponent which generate the area A, B, C. Any of the specificcompositions consisting of an amount of each of the three componentswithin the area A, B, C of FIG. 3 are suitable for melt spinning intohollow-fiber membranes.

In the case of membranes useful for reverse osmosis of liquids, theconcentration of polysulfone is preferably at least about 30 weightpercent, more preferably at least about 35 weight percent. Theconcentration of the solvent is preferably at least about 12 weightpercent, more preferably at least about 20 weight percent. If present,the concentration of the non-solvent is preferably at least about 1weight percent, more preferably at least about 5 weight percent.

The compositions of this invention may be used to fabricate polysulfonesemipermeable membranes useful for “liquid-separation processes.” Asdefined herein, such processes include, but are not limited to,microfiltration, ultrafiltration, dialysis, and reverse osmosis. FIG. 5shows a representative liquid-separation device configured for use as anextracorporeal blood treatment device, specifically a hemodialyzer. Thehemodialyzer 10 comprises an outer casing 12, end caps 14, a dialysateinlet 16, a dialysate outlet 18, a blood inlet 20, a blood outlet 22,and a bundle of fibers 24 potted in the outer casing. The outer casingdefines a dialysate compartment, and the lumina of the fibers form ablood compartment. As blood flows through the lumina of the fibers in aparallel fashion, dialysate flows counter-currently through thedialysate compartment.

Membranes of the present invention may be fabricated by alternativemethod schemes as illustrated in FIGS. 1 and 2. A number of methodschemes may be followed depending upon the optional method steps chosento develop the desired polysulfone membrane.

In one preferred method according to the present invention, apolysulfone composition of polysulfone compound, solvent, and optionalnon-solvent is precompounded in a high-shear mixer, melted, extruded (ashollow fibers), quenched (FIG. 1), and then wound on cores or reelsusing any number of commercially available winders, such as Leesonawinders. In such a method, adequate care should be taken to maintain aslight tension on the hollow fibers during winding. In another preferredmethod according to the present invention, the polysulfone compositionis precompounded in a high-shear mixer, melted, extruded through astrand die (to form solid strands), cooled, pelletized, remelted,extruded (to form hollow fibers), quenched, and then wound (FIG. 2). Instill another preferred method according to the present invention, thepolysulfone composition is precompounded, melted, extruded (as hollowfibers), quenched, wound, held dry for a period of time, soaked in aliquid that is substantially a non-solvent for the polysulfone compoundand stored in the soaking liquid for up to 15 days (FIG. 1). In yetanother preferred method according to the present invention, apolysulfone composition is precompounded in a high-shear mixer, melted,extruded (as hollow fibers), quenched, wound, soaked, leached, rinsed,replasticized, and then dried in an oven (preferably a convection oven)(FIG. 1). In another preferred method according to the presentinvention, the polysulfone composition is precompounded, melted,extruded (as solid strands), cooled, pelletized, remelted, extruded (ashollow fibers), quenched, wound, and then held dry in air followed bysoaking in a liquid that is substantially a non-solvent for thepolysulfone compound (FIG. 2). In yet another preferred method accordingto the present invention, a polysulfone composition is precompounded,melted, extruded (as solid strands), cooled, pelletized, remelted,extruded (as hollow fibers), quenched, wound, soaked, leached, rinsed,replasticized, and dried (FIG. 2).

The components of the composition (i.e., the polysulfone compound,solvent, and optional non-solvent) to be extruded are combined andhomogenized prior to extrusion by mixing in a convenient manner withconventional mixing equipment, as for example, a high-shear mixer, suchas a compounding twin-screw extruder The components of the extrusioncomposition may also be combined and homogenized directly in a meltpotprovided with suitable agitation of the molten liquid. Alternatively, apolysulfone extrusion composition may be homogenized by extruding amolten composition through a strand die, cooling the global extrudate,and grinding or pelletizing the extrudate to a particle size readily-fedto a heated, single-screw or twin-screw extruder. Alternatively, otherheating/homogenizing methods known to those skilled in the art may beutilized to produce a homogeneous, molten liquid for extrusion (termed a“melt”).

The melt is heated to a temperature that facilitates preparation of ahomogeneous liquid possessing a viscosity suitable for extrusion. Thetemperature should not be so high as to cause significant degradation ofthe polysulfone, the solvent, or the non-solvent. The temperature shouldnot be so low as to render the liquid too viscous for extrusion. Forexample, when the melt comprises bisphenol A polysulfone, the extrusiontemperature is preferably at least about 50° C., more preferably atleast about 75° C. The extrusion temperature is preferably less thanabout 300° C., more preferably less than about 220° C.

The viscosity of the melt should not be so high as to be too viscous tobe extruded at temperatures that do not deleteriously affect thepolysulfone compound. The viscosity, however, of the melt must not be solow that the extrudate cannot maintain a desired shape upon exiting theextrusion die. The melt may be extruded in a variety of shapes such as,but not limited to, hollow-fibers, tubes, sheets, and hollow-fibers withfins. The extrudate may be aided in retaining its desired shape uponextrusion by cooling.

For making hollow-fiber membranes, the melt is extruded through ahollow-fiber die (spinneret). The spinneret typically is multi-holedand, thus, produces a tow of multiple hollow fibers. The spinnerettypically includes a means for supplying a fluid (gas or liquid) to thecore or “lumen” of the extrudate. The core fluid is used to preventcollapse of the hollow fibers as they exit the spinneret. The core fluidmay be a gas, such as nitrogen, air, carbon dioxide, or other inert gas,or a liquid which is a non-solvent for the polysulfone compound, suchas, but not limited to, water, poly(ethylene glycol), di(ethyleneglycol), tri(ethylene glycol), glycerol, and mixtures thereof Mixturesof solvents and non-solvents may be used as long as the mixture is not asolvent for the polysulfone compound. Alternatively, the melt may firstbe extruded as solid strands through a single or multi-holed strand dieand the resulting solid strands cooled and pelletized to a particle sizereadily fed to a single-screw or twin-screw extruder (FIG. 2). In thisalternative method of production, the particles are remelted and thenextruded through a single-holed or multi-holed spinneret to form hollowfibers, as described above.

The extrudate exiting extrusion die enters one or more quench zones. Theenvironment of a quench zone may be gaseous or liquid. Within the quenchzone, the extrudate is subjected to sufficient cooling to cause gelationand solidification of the membrane. In an embodiment of the method ofthe present invention, the time period beginning after the extrudateexits the die and extending to before the membrane is wound onto a coreor reel, is important to attain the desired permeability of themembrane. During this time period, for a given composition, thepermeability of the membrane is determined largely by the cooling rateto which the extrudate is subjected. Permeability is increased by rapidquenching of the extrudate, compared to the permeability obtained from aless drastic quench or slower gelling of the extrudate. Increasingpermeability of the membranes, which results from more rapid quenching,normally affects the ability of the membranes to transport water, orother liquids and compounds across the thickness dimension of themembranes. Thus, the extrudate cooling rate (as affected by thetemperature and composition of the cooling medium employed) may bevaried to modify the permeability of the resulting membrane.

In one method according to the present invention, a polysulfonehollow-fiber extrudate is quenched in air. Within the quench zone, thehollow fibers gel and solidify. The temperature of the air-quench zoneis preferably less than about 27° C., more preferably less than about24° C. The hollow fibers are held in the air zone for preferably lessthan about 180 minutes, more preferably less than about 30 minutes.

In another preferred method according to the present invention, thehollow-fiber extrudate is quenched in a liquid that is substantially anon-solvent for the polysulfone compound, such as water, poly(ethyleneglycol), di(ethylene glycol), tri(ethylene glycol), glycerol, or amixture thereof. A mixture of solvent(s) and non-solvent(s)alternatively may be used so long as the mixture remains substantially anon-solvent for the polysulfone compound. When a liquid quench compriseswater and one or more other components, the ratio of water to the othercomponents is preferably from about 0.25:1 to about 200:1. Thetemperature of the liquid quench zone is preferably less than about 50°C., more preferably less than about 25° C., and more preferably lessthan about 10° C. The advantage of a liquid quench is that it offersless resistance to the transfer of heat from the extrudate to thecooling medium than is present in an air quench and, thus, results in amore rapid removal of heat from the extrudate as the membrane forms. Therapid removal of heat modifies the permeability of the resultingmembrane and can be used to tailor membrane permeability for theintended end use.

Hollow fibers are, optionally, drawn using godet rollers or otherconventional equipment to the appropriate fiber diameter. Morespecifically, drawing or stretching the fiber may be accomplished bypassing the hollow fiber over a series of rollers. The desired degree ofstretching may be obtained by control of the rate of rotation of thesecond roller or second group of rollers relative to the first rollerencountered by the fiber. Line speeds are generally not critical and mayvary over a wide range. Preferred line speeds are at least about 10 feetper minute and less than about 1000 feet per minute.

In another preferred method according to the present invention, asillustrated in FIG. 2, following quenching, the membrane is passedthrough at least one leach bath containing a liquid that issubstantially a non-solvent for the polysulfone compound, such as wateror a mixture of water and sulfolane and/or the non-solvent(s), or amixture of water and the solvent utilized in the melt composition. Goodresults have been achieved when the leach bath is water. The membrane isleached to remove at least a portion of the solvent and the non-solvent.The leach bath need not remove all of the solvent and non-solvent fromthe membrane, depending, at least in part, on the anticipated end use ofthe membrane.

The minimum temperature of the leach bath is such that removal of thesolvent and non-solvent from the membrane occurs at a reasonable raterelative to production rate demands. The minimum temperature of theleach bath is preferably at least about 20° C., more preferably at leastabout 40° C. The maximum temperature of the leach bath is below atemperature at which the integrity of the membrane is deleteriouslyaffected. Accordingly, the temperature of the leach bath is preferablyless than about 95° C.

By way of example, the residence time of a hollow-fiber membrane in theleach bath is preferably less than about 1200 seconds, more preferablyless than about 300 seconds. The hollow fiber may, optionally, be drawnto the desired size prior to entrance into the leach bath, during theresidence time in the leach bath, subsequent to exiting the leach bath,or during any combination thereof.

Following immersion in the leach bath, the membrane may, optionally, bepassed through a rinse bath containing water. The rinse bath removesresidues in the membrane from the leach process. The rinse bath ispreferably maintained at room temperature. For a hollow fiber, theresidence time of the fiber within the rinse bath is preferably lessthan 1200 seconds, more preferably less than 300 seconds.

After leaching, the membrane may then be subjected to a replasticizationprocess. For hollow-fiber membranes to be used for dialysis, areplasticization bath is used that preferably contains less than about50 weight percent glycerol and more preferably less than about 45 weightpercent glycerol, with the balance being water. The minimum temperatureof the replasticization bath is such that replasticization of themembrane occurs at reasonable rate relative to production demands. Forexample, the minimum temperature of a glycerol-containingreplasticization bath is preferably at least about 20° C., morepreferably at least about 35° C. The maximum temperature of thereplasticization bath is below a temperature at which the membraneintegrity could be adversely affected. Accordingly, the maximumtemperature of the replasticization bath is preferably less than about100° C., more preferably less than about 50° C.

Following removal of the membrane from the replasticization bath, excessliquid adhering to the membrane may optionally be removed, preferably byuse of a conventional air knife operating at a pressure of about 10 psigto about 60 psig. With hollow fibers, good results have been achievedwhen the air knife is maintained at a pressure of about 30 psig.

The resulting polysulfone membrane may, optionally, be dried in an oven(preferably a convection oven). The oven is maintained at a temperatureof from about 20° C. to about 200° C. With hollow fibers, good resultshave been achieved when the temperature of the oven is about 70° C. In aconvection oven the membrane is dried for a period of from about 5seconds to about 1200 seconds. With hollow fibers, good results havebeen achieved when the fiber was dried for at least about 140 seconds.

The semipermeable polysulfone membranes formed by the described methodsmay be used in liquid-separation processes such as, but not limited to,microfiltration, ultrafiltration, dialysis, and reverse osmosis. Thespecific fabrication method that is employed, within the scope ofmethods according to the present invention, is selected so as to tailorthe resulting membrane for its anticipated end use. Such adaption isreadily achieved by one skilled in the art based upon the teachingsherein.

The following various examples are presented to illustrate the inventiononly and are not intended to limit the scope of the invention or thefollowing claims.

EXAMPLE 1

A composition was prepared comprising about 36 weight percent UdelP1835NT11, a brand of bisphenol A polysulfone (available from AmocoPolymers, Inc. of Alpharetta, Ga.) about 44.3 weight percent anhydroussulfolane (available from Phillips Chemical Company of Borger, Tex.) andabout 17.7 weight percent poly(ethylene glycol) having an averagemolecular weight of about 1000 daltons (available from Dow ChemicalCompany of Midland, Mich.). The solvent to non-solvent ratio was about4.5:1. The composition was compounded in a co-rotating twin-screwextruder at about 132° C. The extruded composition was cooled,pelletized using an RCP 2.0 pelletizer (available from RandcastleExtrusion Systems, Inc., of Cedar Grove, N.J.), and then remelted andextruded through a 30-hole hollow-fiber spinneret at about 149° C. usinga single-screw extruder. The resulting hollow-fiber extrudate wasquenched in air at about 21° C. for about 15 seconds, drawn from a firstgodet (rotating at a surface speed of 172 feet per minute) to a secondgodet (rotating at a surface speed of 182 feet per minute) to increasethe fiber's length by about 5.75 percent, wound on a core, and soaked ina water bath at a temperature of about 25° C. for about four hours.

Following soaking in water, the hollow fiber was processed by unwindingthe fiber from the core at a rate of about 30 ft/min and passing thefiber through a 37° C. water bath for about 40 seconds. The fiber wasthen immersed in a room temperature water-rinse bath for 139 seconds.Following the rinse bath, the fiber was replasticized by immersion for140 seconds in a 40-percent aqueous glycerol replasticization bath heldat about 37° C. After removing the fiber from the aqueous glycerol bath,excess liquid was removed from the fiber using an air knife operating atabout 30 psig. The processed hollow fiber was then dried in a convectionoven at about 70° C. for 155 seconds.

The resulting hollow fiber had an average lumen diameter of 160 μm, andan average wall thickness of 18 μm. The hollow fiber was fabricated intoa dialysis test unit containing 150 fibers. The in vitro water flux ofthe device was 102.5 mL/(hr.mmHg.m²) and the average K_(ov) for sodiumchloride was found to be 1.92×10⁻² centimeters per minute at a solutionflow rate through the fiber lumina of about 0.02 milliliters per minuteper fiber. K_(ov) is defined in the following equation:$\frac{1}{K_{ov}} = {\frac{1}{K_{b}} + \frac{1}{P_{m}}}$where K_(b) is the resistance to mass transfer within the fluid presentin the lumen of the hollow fiber, and P_(m) is the membranepermeability. It was not possible to determine the membranepermeability, P_(m), alone using the test apparatus because the flow ofsolution through an individual fiber could not be made large enough torender K_(b) negligible.

This hollow-fiber membrane could be fabricated into a suitable devicefor use as an ultrafiltration cell for the removal of contaminants fromwater or aqueous solutions.

EXAMPLE 2

A composition was prepared comprising about 36 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 45.7 weight percentanhydrous sulfolane (Phillips Chemical), and about 18.3 weight percentpoly(ethylene glycol) having an average molecular weight of about 1000daltons (Dow Chemical), yielding a solvent to non-solvent ratio about2.5:1. The composition was compounded in a co-rotating, twin-screwextruder at about 173° C. The extruded composition was then pelletized,remelted, and extruded through a 30-hole hollow-fiber spinneret at about178° C. using a single-screw extruder. The resulting hollow-fiberextrudate was quenched in air at about 22° C. for 7-8 seconds. Theresulting hollow-fiber membrane was wound on a core at about 110 feetper minute, and held dry for about one hour. The hollow fiber was thenplaced in a water bath maintained at a temperature of about 25° C. for aperiod of about 12-15 hours.

The hollow fiber was then processed by unwinding from the core at about30 ft/min and passing the fiber through a 36° C. water leach bath forabout 40 seconds. The fiber was immersed in a room temperaturewater-rinse bath for 139 seconds. The fiber was replasticized for 140seconds in a 37° C. bath of about 40 weight percent aqueous glycerol.After removing the fiber from the aqueous glycerol bath, excess liquidwas stripped from the fiber using an air knife operating at a pressureof about 30 psig. The processed fiber was then dried in a convectionoven at about 70° C. for 155 seconds.

The resulting hollow fiber bad an average lumen diameter of about 142μm, and an average wall thickness of about 31 μm. Dialysis test unitseach containing 150 of the hollow fibers were fabricated. The average invitro water flux of these devices was 68.0 mL/(hr.mmmHg.m²) and theaverage K_(ov) for sodium chloride was about 2.28×10⁻² centimeters perminute at a solution flow rate through the fiber lumina of about 0.02milliliters per minute per fiber. This hollow-fiber membrane is usefulfor ultrafiltration, such as for use in an ultrafiltration cell for theremoval of contaminants from water or aqueous solutions.

EXAMPLE 3

A composition was prepared comprising about 38 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 44.3 weight percentanhydrous sulfolane (Phillips Chemical), and about 17.7 weight percentpoly(ethylene glycol) having an average molecular weight of about 1000daltons (Dow Chemical), yielding a solvent to non-solvent ratio of about4.5:1. The composition was compounded in a co-rotating, twin-screwextruder at about 99° C., and extruded directly through a 30-holehollow-fiber spinneret. The extrudate was quenched in air at about 26°C. for about 6 seconds. The resulting hollow-fiber membrane was wound ona core at about 160 feet per minute, and placed immediately into a waterbath for a period of about 12-15 hours.

The hollow fiber was then unwound from the core at about 30 ft/min andpassed through a 37° C. water leach bath for about 40 seconds. The fiberwas then immersed in a room-temperature water rinse bath for about 140seconds. The fiber was replasticized for 140 seconds in an aqueousglycerol bath containing about 40 weight percent glycerol, the bathbeing held at about 38° C. After removing the fiber from the aqueousglycerol bath, excess liquid was removed from the fiber by an air knifeoperating at a pressure of about 30 psig. The fiber was then dried in aconvection oven at about 70° C. for about 155 seconds.

The resulting hollow-fiber membrane had an average lumen diameter of 237μm, and an average wall thickness of 35 μm. Dialysis test units eachcontaining 150 of the resulting fibers were fabricated from this fiber.The average in vitro water flux of these devices was 143.5mL/(hr.mmHg.m²) and the average K_(ov) for sodium chloride was found tobe 0.88×10⁻² centimeters per minute at a solution flow rate through thefiber lumina of about 0.02 milliliters per minute per fiber. Thishollow-fiber membrane can be used in an ultrafiltration cell for theremoval of contaminants from water or aqueous solutions.

EXAMPLE 4

A composition was prepared comprising about 38 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 45.7 weight percentanhydrous sulfolane (Phillips Chemical), and about 18.3 weight percentpoly(ethylene glycol) having an average molecular weight of about 1000daltons (Dow Chemical), yielding a solvent to non-solvent ratio of about2.5:1. The composition was compounded in a co-rotating twin-screwextruder at about 143° C., and extruded directly through a 30-holehollow-fiber spinneret. The 20 extrudate was quenched in air at about25° C. for about 0.08 minutes, wound on a core at about 203 feet perminute, and held dry for thirty minutes before being placed in a 25° C.water bath for about three days.

The hollow fiber was then unwound from the core at about thirty feet perminute and passed through a 38° C. water-leach bath for about thirtyseconds. The fiber was immersed in a room temperature water rinse bathfor 148 seconds. The fiber was replasticized for 149 seconds in anaqueous glycerol bath containing about 40 weight percent glycerol, thebath being held at about 38° C. After removing the fiber from theaqueous glycerol bath, excess liquid was removed from the fiber using anair knife operating at a pressure of about thirty psig. The processedhollow fiber was dried in a convection oven at about 70° C. for 147seconds.

The resulting hollow-fiber membrane had an average lumen diameter of 192μm, and an average wall thickness of 29.5 μm. Dialysis test units eachcontaining 150 of the resulting fibers were fabricated. The average invitro water flux of these devices was 141.2 mL/(hr.mmHg.m²) and theaverage K_(ov) for sodium chloride was found to be 1.20×10⁻² centimetersper minute at a solution flow rate through the fiber lumina of about0.02 milliliters per minute per fiber. This hollow-fiber membrane isuseful in an ultrafiltration cell for the removal of contaminants fromwater or aqueous solutions.

EXAMPLE 5

A composition was prepared comprising about 34 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 54 weight percentanhydrous sulfolane (Phillips Chemical Company), about 11 weight percentpoly(ethylene glycol) having an average molecular weight of about 1000daltons (Dow Chemical Company), and about 1 weight percent glycerol(VanWaters & Rogers, Inc., Seattle, Wash.), yielding a solvent tonon-solvent ratio of about 4.5:1. The composition was compounded in aco-rotating twin-screw extruder at about 144° C. The extrudate was thencooled, pelletized, remelted, and extruded through a 30-holehollow-fiber spinneret at about 134° C. using a single-screw extruder.The resulting extrudate was quenched in air at about 20° C. for about0.08 minute, and wound on a core at about 200 feet per minute. Theentire wound core was immediately placed in a 25° C. water bath for aperiod of about 15-20 hours.

The hollow fiber was then processed by unwinding the fiber from the coreat about 30 feet per minute and passing the fiber through aroom-temperature water-leach bath for 97 seconds. The fiber wasreplasticized for 145 seconds in a bath containing about 40 weightpercent aqueous glycerol held at about 38° C. After removing the fiberfrom the aqueous glycerol bath, excess liquid was stripped from thefiber using an air knife operating a pressure of about 30 psig. Theprocessed hollow fiber was dried in a convection oven at about 62° C.for 151 seconds.

The resulting hollow-fiber membrane had an average lumen diameter ofabout 165 μm, and an average wall thickness of about 18 μm. Test unitseach containing about 150 of the resulting fibers were fabricated. Theaverage in vitro water flux of these devices was 67.2 mL/(hr.mmHg.m²)and the average K_(ov) for sodium chloride was found to be 2.19×10⁻²centimeters per minute at a solution flow rate through the fiber luminaof about 0.02 milliliters per minute per fiber.

EXAMPLE 6

A composition was prepared comprising about 34 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 54 weight percentanhydrous sulfolane (Phillips Chemical Company), about 6 weight percentpoly(ethylene glycol) having an average molecular weight of about 1000daltons (Dow Chemical Company) and about 6 weight percent tri(ethyleneglycol) (Aldrich Chemical Company, Inc., Milwaukee, Wis.), yielding asolvent to non-solvent ratio of about 4.5:1. The composition wascompounded in a co-rotating, twin-screw extruder at about 153° C. Theextrudate was then cooled, pelletized, remelted, and extruded through a30-hole hollow-fiber spinneret at about 137° C. using a single-screwextruder. The resulting hollow-fiber extrudate was quenched in air atabout 20° C. for 0.08 minute, and wound on a core at about 200 feet perminute. The entire fiber core was immediately placed in a 25° C. waterbath for a period of 15-20 hours.

The hollow fiber was then processed by unwinding the fiber from the coreat about 30 feet per minute and passing the fiber through aroom-temperature water-leach bath for 95 seconds. The fiber was thenimmersed in a room-temperature water-rinse bath for 134 seconds. Thehollow fiber was replasticized for 146 seconds in a bath of about 40weight percent aqueous glycerol held at about 38° C. After removing thefiber from the aqueous glycerol bath, excess liquid was stripped fromthe fiber using an air knife operating at a pressure of about 30 psig.The processed hollow fiber was dried in a convection oven at about 70°C. for 150 seconds.

The resulting hollow-fiber membrane had an average lumen diameter ofabout 180 μm, and an average wall thickness of about 20 μm. Test unitseach containing about 150 of the resulting fibers were fabricated. Theaverage in vitro water flux of these devices was 60.0 mL/(hr.mmHg.m²)and the average K_(ov) for sodium chloride was found to be 2.17×10⁻²centimeters per minute at a solution flow rate through the fiber luminaof about 0.02 milliliters per minute per fiber.

EXAMPLE 7

A composition was prepared comprising about 32 weight percent UdelP1835NT11 polysulfone (Amoco Polymers, Inc.), about 53 weight percentanhydrous sulfolane (Phillips Chemical Company), and about 15 weightpercent poly(ethylene glycol) having an average molecular weight ofabout 1000 daltons (Dow Chemical Company), yielding a solvent tonon-solvent ratio of about 2.5:1. The composition was compounded in aco-rotating twin-screw extruder at about 131° C. and extruded directlythrough a 30-hole hollow-fiber spinneret. The extrudate was quenched inwater at about 7° C. for about 6 seconds. The resulting hollow-fibermembranes were wound on a core at about 244 feet per minute. The entirefiber core was immediately placed in a 25° C. water bath for a period ofabout 15-20 hours.

The hollow fibers were then processed by unwinding the fibers from thecore at about 30 feet per minute and passing the fibers through aroom-temperature water-leach bath for 97 seconds. The fibers were thenimmersed in a room-temperature water-rinse bath for 135 seconds. Thefibers were replasticized for 146 seconds in a bath of about 40 weightpercent aqueous glycerol, the bath being held at about 38° C. Afterremoving the fibers from the aqueous glycerol bath, excess liquid wasstripped from the fiber using an air knife operating at a pressure ofabout 20 psig. The processed fibers were dried in a convection oven atabout 45° C. for about 152 seconds.

The resulting hollow-fiber membranes had an average lumen diameter ofabout 203 μm, and an average wall thickness of about 37 μm. Test unitseach containing about 150 of the resulting fibers were fabricated. Theaverage in vitro water flux of these devices was 9.1 mL/(hr.mmHg.m²) andthe average K_(ov) for sodium chloride was found to be 1.76×10⁻²centimeters per minute at a solution flow rate through the fiber luminaof about 0.02 milliliters per minute per fiber.

Having illustrated and described the principles of the invention withseveral preferred embodiments and multiple various examples, it shouldbe apparent to those skilled in the art that the invention can bemodified in arrangement and detail without departing from suchprinciples. We claim all the modifications coming within the spirit andscope of the following claims.

1. A melt-spun polysulfone semipermeable membrane, the melt-spunpolysulfone semipermeable membrane consisting essentially of apolysulfone compound and a solvent for the polysulfone compound whereinthe melt-spun polysulfone semipermeable membrane has a homogeneousstructure such that the melt-spun polysulfone semipermeable membrane hasa substantially uniform pore structure through a thickness of themelt-spun polysulfone semipermeable membrane; wherein the solvent isselected from the group consisting of tetramethylene sulfone,antipyrine, δ-valerolactam, diethylphthalate, and mixtures thereof. 2.The melt-spun polysulfone semipermeable membrane of claim 1, wherein thepolysulfone compound is selected from the group consisting of apolyarylsulfone compound, bisphenol A polysulfone, polyetherpolysulfone, polyphenyl polysulfone, and mixtures thereof.
 3. Apolysulfone semipermeable membrane defined by a composition consistingessentially of a mixture of a polysulfone compound, a solvent for thepolysulfone compound, and a non-solvent for the polysulfone compoundwherein the mixture has been melt-spun allowing a homogeneous structureto be formed such that the polysulfone semipermeable membrane has asubstantially uniform pore structure throughout a thickness of thepolysulfone semipermeable membrane.
 4. The polysulfone semipermeablemembrane of claim 3, wherein the polysulfone compound is selected fromthe group consisting of a polyarylsulfone compound, bisphernol Apolysulfone, polyether polysulfone, polyphenyl polysulfone, and mixturesthereof.
 5. The polysulfone semipermeable membrane of claim 3, whereinthe polysulfone semipermeable membrane includes between about 8 andabout 80 percent by weight of the polysulfone compound.
 6. Thepolysulfone semipermeable membrane of claim 3, wherein the polysulfonesemipermeable membrane includes at least about 25 percent by weight ofthe polysulfone compound.
 7. The polysulfone semipermeable membrane ofclaim 3, wherein the solvent is selected from the group consisting oftetramethylene sulfone, 3-methyl sulfolane, benzophenone,n,n-dimethylacetamide, 2-pyrrolidone, 3-methylsulfolene, pyridine,thiophene, o-dichlorobenzene, 1-chloronaphthalene, methyl salicylate,anisole, o-nitroanisole, diphenyl ether, diphenoxy methane,acetophenone, p-methoxyphenyl-2-ethanol, 2-piperidine, antipyrine,δ-valerolactam, diethyl phthalate, diphenyl sulfone, diphenyl sulfoxide,phthalic acid, dioctyl ester, phthalic acid, dimethyl ester, phthalicacid, diethyl ester, phthalic acid, dibutyl ester, phthalic acid,bis(2-ethylhexyl) ester, phthalic acid, benzyl butyl ester, phenylsulfide, and mixtures thereof.
 8. The polysulfone semipermeable membraneof claim 3, wherein the solvent is selected from the group consisting oftetramethylene sulfone, antipyrine, δ-valerolactam, diethyl phthalate,and mixtures thereof.
 9. The polysulfone semipermeable membrane of claim3, wherein the non-solvent is selected from the group consisting of 1,1-diethylurea, 1,3-diethylurea, dinitrotoluene, 1,2-ethane diamine,diphenylamine, toluenediamine, o-toluic acid, m-toluic acid,toluene-3,4-diamine, dibutyl phthalate, piperidine, decalin,cyclohexane, cyclohexene, chlorocyclohexane, cellosolve solvent,n,n-dimethylbenzylamine, paraffin, mineral oil, mineral wax, tallowamine, triethanol amine, lauryl methacrylate, stearic acid, di(ethyleneglycol), tri(ethylene glycol), ethylene glycol, poly(ethylene glycal),tetra(ethylene glycol), glycerin, diethyl adipate, d-sorbitol,chlorotriphenyl stannane, resorcinol, 2-methyl-8-quinolinol, quinaldine,4-phenylpyridine, phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl)ester, N,N-dimethyl-p-phenylene diamine, 2, 6-dimethoxyphenol,4-allyl-2-methoxyphenol, phenanthridine, 2-naphthylamine,1-naphthylamine, 1-naphthol, 2-naphthalenethiol, 1-bromonaphthalene,levulinic acid, phenyl pyrrol-2-yl ketone, phenyl 4-pyridyl ketone,isothiocyanic acid, m-nitrophenyl ester, 2-methyl-1H-indole, 4-methylimidazole, imadazole, 1,7-heptanediol, 9H-fluoren-9-one, ferrocene,2,2′,2″-nitrilotriethanol, 2,2′-iminodiethanol, dibenzofuran,cyclohexaneacetic acid, cyanamide, courmarin, 2,2′-bipyridine, benzoicacid, benzenepropionic acid, o-dinitrobenzene,9-methyl-9-azabicyclo(3.3.1)nonan-3-one, chlorodiphenylarsine, antimonybromide, p-anisidine, o-anisaldehyde, adiponitrile, p-aminoacetophenone, monoacetin, diacetin, triacetin, pentoxane,4-benzoylbiphenyl, methyl oleate, triethylphosphate, butyrolactone,terphenyl, tetradecanol, polychlorinated biphenyl, myristic acid,methacrylic acid, dodecyl ester, isocyanic acid, methylenedi-p-phenyleneester, 2-((2-hexyloxy)ethoxy) ethanol, 4-nitro biphenyl, benzyl ether,benzenesulfonyl chloride, 2,4-diisocyanato-1-1-methyl benzene, adipicacid, diethyl ester, 2′-nitro-acetophenone, 1′-acetonaphthone,tetradecanone, (dichlorophenyl)trichlorosilane, dichlorodiphenyl silane,phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester, phosphoricacid, tri-o-tolyl ester, phosphoric acid, triphenyl ester, phosphoricacid, tributyl ester, phenyl phosphorous dichloride, p-nitrophenol,isocyanic acid, methyl-m-phenylene ester, 2,2′-iminodiethanol,N-(2-aminoethyl)-N′-(2-((2-aminoehtyl)amino)ethyl) 1,2-ethanediamine,2,6-di-tert-butyl p-cresol, chloro biphenyl, 4-biphenylamine, benzylether, benzenesulfonyl chloride, 1,2-(methylenedioxy)-4-propenylbenzene, 2,4-diisocyanato-1-methyl benzene, chlorodinitro benzene (mixedisomers), hexahydro 2H-azepin-2-one, 4,4′-methylenedianiline,1′-acetonaphthone, mercapto acetic acid, acetanilide, glycerol, andmixtures thereof.
 10. The polysulfone semipermeable membrane of claim 3,wherein the solvent and non-solvent are present in a ratio of about 2:1to about 10:1.
 11. The polysulfone semipermeable membrane of claim 3wherein the polysulfone compound is composed of bisphenol A polysulfone,wherein the solvent is composed of sulfolane, and wherein thenon-solvent is composed of poly(ethylene glycol).
 12. The polysulfonesemipermeable membrane of claim 11 wherein the composition includesabout 30% by weight to about 38% by weight of the polysulfone compound.13. A polysulfone semipermeable membrane having a substantially uniformpore structure throughout a thickness dimension of the polysulfonesemipermeable membrane, the polysulfone semipermeable membrane beingconstructed from a melt-spun composition consisting essentially of apolysulfone compound, a solvent for the polysulfone compound selectedfrom the group consisting of tetramethylene sulfone, antipyrine,6-valerolactam, diethyl phthalate, and mixtures thereof, and anon-solvent.
 14. The polysulfone semipermeable membrane of claim 13,wherein the non-solvent is selected from the group consisting of 1,1-diethylurea, 1,3-diethylurea, dinitrotoluene, 1,2-ethane diamine,diphenylamine, toluenediamine, o-toluic acid, m-toluic acid,toluene-3,4-diamine, dibutyl phthalate, piperidine, decalin,cyclohexane, cyclohexene, chlorocyclohexane, cellosolve solvent,n,n-dimethylbenzylamine, paraffin, mineral oil, mineral wax, tallowamine, triethanol amine, lauryl methacrylate, stearic acid, di(ethyleneglycol), tri(ethylene glycol), ethylene glycol, poly(ethylene glycol),tetra(ethylene glycol), glycerin, diethyl adipate, d-sorbitol,chlorotriphenyl stannane, resorcinol, 2-methyl-8-quinolinol, quinaldine,4-phenylpyridine, phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl)ester, N,N-dimethyl-p-phenylene diamine, 2, 6-dimethoxyphenol,4-allyl-2-methoxyphenol, phenanthridine, 2-naphthylamine,1-naphthylamine, 1-naphthol, 2-naphthalenethiol, 1-bromonaphthalene,levulinic acid, phenyl pyrrol-2-yl ketone, phenyl 4-pyridyl ketone,isothiocyanic acid, m-nitrophenyl ester, 2-methyl-1H-indole, 4-methylimidazole, imadazole, 1,7-heptanediol, 9H-fluoren-9-one, ferrocene,2,2′,2″-nitrilotriethanol, 2,2′-iminodiethanol, dibenzofuran,cyclohexaneacetic acid, cyanamide, courmarin, 2,2′-bipyridine, benzoicacid, benzenepropionic acid, o-dinitrobenzene,9-methyl-9-azabicyclo(3.3.1)nonan-3-one, chlorodiphenylarsine, antimonybromide, p-anisidine, o-anisaldehyde, adiponitrile, p-aminoacetophenone, monoacetin, diacetin, triacetin, pentoxane,4-benzoylbiphenyl, methyl oleate, triethylphosphate, butyrolactone,terphenyl, tetradecanol, polychlorinated biphenyl, myristic acid,methacrylic acid, dodecyl ester, isocyanic acid, methylenedi-p-phenyleneester, 2-((2-hexyloxy)ethoxy) ethanol, 4-nitro biphenyl, benzyl ether,benzenesulfonyl chloride, 2,4-diisocyanato-1-1-methyl benzene, adipicacid, diethyl ester, 2′-nitro-acetophenone, 1′-acetonaphthone,tetradecanone, (dichlorophenyl)trichlorosilane, dichlorodiphenyl silane,phosphorothioic acid, o,o-diethyl o-(p-nitrophenyl) ester, phosphoricacid, tri-o-tolyl ester, phosphoric acid, triphenyl ester, phosphoricacid, tributyl ester, phenyl phosphorous dichloride, p-nitrophenol,isocyanic acid, methyl-m-phenylene ester, 2,2′-iminodiethanol,N-(2-aminoethyl)-N′-(2-((2-aminoehtyl)amino)ethyl) 1,2-ethanediamine,2,6-di-tert-butyl p-cresol, chloro biphenyl, 4-biphenylamine, benzylether, benzenesulfonyl chloride, 1,2-(methylenedioxy)-4-propenylbenzene, 2,4-diisocyanato-1-methyl benzene, chlorodinitro benzene (mixedisomers), hexahydro 2H-azepin-2-one, 4,4′-methylenedianiline,1′-acetonaphthone, mercapto acetic acid, acetanilide, glycerol, andmixtures thereof.
 15. The polysulfone semipermeable membrane of claim13, wherein the polysulfone compound is selected from the groupconsisting of a polyarylsulfone compound, bisphenol A polysulfone,polyether polysulfone, polyphenyl polysulfone and mixtures thereof. 16.The polysulfone semipermeable membrane of claim 13, wherein the solventand non-solvent are present in a ratio of about 2.5:1 to about 4.5:1.17. The polysulfone semipermeable membrane of claim 16 wherein thepolysulfone compound is composed of bisphenol A polysulfone, wherein thesolvent is composed of sulfolane, and wherein the non-solvent iscomposed of poly(ethlene glycol).
 18. The polysulfone semipermeablemembrane of claim 16 wherein the melt-spun composition includes about 30to about 38 percent by weight of the polysulfone compound.